Little Ice Age (Asia) -- Summary
In an aggressive attempt to rewrite climatic history, certain scientists have claimed the Little Ice Age and Medieval Warm Period were neither global phenomena nor strong enough where they did occur to have a discernable influence on mean global air temperature. By doing so, they have made the putative warming of the last part of the 20th century appear highly unusual, which they equate with anthropogenic-induced, which they associate with the historical rise in the air's CO2 content, which gives them reason to call for dramatic reductions in the use of fossil fuels, which we believe to be unwarranted. Hence, we continually search the emerging scientific literature for new evidence that the Little Ice Age and Medieval Warm Period were truly significant global events. This brief review thus summarizes what we have learned over the past few years about the Little Ice Age in Asia.

Starting with Russia, Naurzbaev and Vaganov (2000) developed a proxy temperature record based on tree rings obtained from the cores of 118 trees near the upper timberline in Siberia for the period 212 BC to AD 1996, noting that fluctuations in average annual temperature from the Siberian record were found to agree well with air temperature variations reconstructed from Greenland ice core data, suggesting to them that "the tree ring chronology of [the Siberian] region can be used to analyze both regional peculiarities and global temperature variations in the Northern Hemisphere." In further analyzing their data, they observed the presence of the Medieval Warm Period from about AD 850 to 1150, the cooling of the Little Ice Age from 1200 though 1800, followed by the recovery warming of the 20th century. With respect to this latter warming, they report it is "not extraordinary" and that "the warming at the border of the first and second millennia [AD 1000] was longer in time and similar in amplitude."

In the Middle Ural Mountains of Russia, Demezhko and Shchapov (2001) used borehole data to develop a temperature history that revealed the existence of a number of climatic excursions, including the "Medieval Warm Period with a culmination about 1000 years ago and Little Ice Age 200-500 years ago." They also determined the mean temperature of the Medieval Warm Period was more elevated above the mean temperature of the past century than the mean temperature of the Little Ice Age was reduced below that of the past century.

Analyzing a much greater array of information drawn from written historical evidence, as well as glaciological, hydrological, dendrological, archaeological and palynological data, Krenke and Chernavskaya (2002) report large differences in a number of climatic variables between the period of the Little Ice Age and the preceding Medieval Warm Period in Russia. With respect to the annual mean temperature of northern Eurasia, they report a Medieval Warm Period to Little Ice Age drop on the order of 1.5°C. They also note that the frequency of severe winters increased from once in 33 years in the Medieval Warm Period to once in 20 years in the Little Ice Age, additionally noting that the abnormally severe winters of the Little Ice Age were associated with the spread of Arctic air masses over the entire Russian Plain. Finally, the two members of the Russian Academy of Sciences note that the data they used to draw these conclusions were "not used in the reconstructions performed by Mann et al. (1999)," which perhaps explains why the Mann et al. temperature history of the past millennium does not reproduce the Little Ice Age nearly as well as does the more appropriately derived temperature history of Esper et al. (2002a). And in contradiction of another of Mann et al.'s contentions, the Russian scientists unequivocally state, based on the results of their comprehensive study of the relevant scientific literature, that "the Medieval Warm Period and the Little Ice Age existed globally."

Dropping down into China, Hong et al. (2000) developed a 6000-year high-resolution ð18O record from cellulose deposited in a peat bog in the Jilin Province of China from which they inferred the temperature history of that location over the past six millennia. In comparing this record with a previously-derived ð14C tree-ring record representative of the intensity of solar activity, they also found there was "a remarkable, nearly one to one, correspondence between the changes of atmospheric ð14C and the variation in ð18O of the peat cellulose," implying that the climate changes they observed had been "forced mainly by solar variability." And among the likely solar-induced climate regimes they detected was "an obvious warm period represented by the high ð18O from around AD 1100 to 1200, which may correspond to the Medieval Warm Epoch of Europe," which was followed by a cooler Little Ice Age.

In a somewhat similar study, Xu et al. (2002) examined plant cellulose ð18O variations in cores retrieved from peat deposits west of Hongyuan County at the northeastern edge of the Qinghai-Tibetan Plateau. Following the demise of the Roman Warm Period, they detected three consistently cold events centered at approximately AD 500, 700 and 900, during the Dark Ages Cold Period. Then, from AD 1100-1300, they report "the ð18O of Hongyuan peat cellulose increased, consistent with that of Jinchuan peat cellulose and corresponding to the 'Medieval Warm Period'." Finally, they note that "the periods AD 1370-1400, 1550-1610, [and] 1780-1880 recorded three cold events, corresponding to the 'Little Ice Age'."

Also in China, Chen et al. (2000) studied sediment cores from Erhai Lake, which is located on the Yun-Gui Plateau, reconstructing a temperature history of that region for the 700-year period 1290-1990. The two coldest intervals of this period occurred during the 14th century and from about 1550 to 1800. Of the latter cold period, Chen et al. say in their abstract that it "may be the imprint left of the Little Ice Age." And to be sure we get the point, they repeat this statement twice more in the text of their paper. Hence, it would be safe to say they do not subscribe to the climate-alarmist view that the Little Ice Age was confined to countries bordering on the North Atlantic Ocean. Also, their statement that "the global warming at the beginning of this century continued until the 1940s" does not bode well for the climate-alarmist claim of "unprecedented" warming over the latter part of the 20th century.

Qian and Zhu (2002) present an analysis of several data sets related to Holocene climate change in China, one of which is an 1100-year record of annual calcite accumulation derived by Qin et al. (1999) from a stalagmite found in Shihua Cave, Beijing. The thickness sequence of laminae in this stalagmite, which is a measure of the hydrologic balance of the surrounding area, reveals the existence of a relatively wet Medieval Warm Period running from approximately AD 940 to 1200 and a relatively dry Little Ice Age that was most strongly expressed between 1400 and 1800. One of the driving forces behind the authors' study was, as they put it, "the question of whether warming similar to the recent occurred before the Little Ice Age." Their analysis of the Beijing stalagmite data indicates that most of the AD 940 to 1200 period was indeed equivalent to the most outstanding portions of the 20th century with respect to moisture availability, suggesting that temperatures may well have been equivalent too.

Further south, Paulsen et al. (2003) used high-resolution records of ð13C and ð18O in a stalagmite from Buddha Cave (33°40'N, 109°05'E) to infer changes in climate in central China for the last 1270 years in terms of warmer, colder, wetter and drier conditions. Among the climatic episodes evident in their data were "those corresponding to the Medieval Warm Period, Little Ice Age and 20th-century warming, lending support to the global extent of these events." Specifically, their record begins in the depths of the Dark Ages Cold Period, which ends about AD 965 with the commencement of the Medieval Warm Period, which continues to approximately AD 1475, whereupon the Little Ice Age sets in and holds sway until about AD 1825, after which the warming responsible for the Modern Warm Period begins.

In tropical South China, Chu et al. (2002) studied the geochemistry of dated sediments recovered from seven cores taken from three locations in Lake Huguangyan on the low-lying Leizhou Peninsula, assisted by additional information relative to the presence of snow, sleet, frost and frozen rivers over the past 1000 years obtained from historical documents. They report that "cold winter events over the past 1000 years in tropical South China are concentrated in three time intervals during the Little Ice Age at c. AD 1480-1550, 1670-1730 and 1830-1900," noting further that this distribution of cold events agrees well with results obtained from phenological studies (flowing seasons of peach, apricot, clove, etc.), which depict cold intervals at AD 1470-1520, 1620-1720 and 1840-1890 (Chu, 1973). They additionally report that "recent publications based on the phenological phenomena, distribution patterns of subtropical plants and cold events (Wang and Gong, 2000; Man, 1998; Wu and Dang, 1998; Zhang, 1994) argue for a warm period from the beginning of the tenth century AD to the late thirteenth century AD," as their own data also suggest. Their data further indicate that floods were quite common during the Little Ice Age, while two major dry periods occurred during the Medieval Warm Period, noting that "local historical chronicles support these data and suggest that the climate of tropical South China was dry during the 'Mediaeval Warm Period' and wet during the 'Little Ice Age'."

The last China study we have reviewed, which is perhaps the most comprehensive of all, is that of Yang et al. (2002), who used nine separate proxy climate records derived from peat, lake sediment, ice core, tree ring and other proxy sources to compile a single weighted temperature history for the entire country spanning the past two millennia. This record revealed five distinct climate epochs: a warm stage from AD 0 to 240 (the latter part of the Roman Warm Period), a cold interval between AD 240 and 800 (the Dark Ages Cold Period), a return to warm conditions from AD 800-1400 (which included the Medieval Warm Period between AD 800 and 1100), a cool interval between 1400 and 1820 (the Little Ice Age), and the current warm regime (the Modern Warm Period), which has so far not been the warmest of the three warm periods. That distinction is held by the Roman Warm Period during the second and third centuries AD.

Dropping still further south, Esper et al. (2002b) employed more than 200,000 ring-width measurements from 384 trees obtained from 20 individual sites ranging from the lower to upper timberline in the Northwest Karakorum of Pakistan and the Southern Tien Shan of Kirghizia to reconstruct regional patterns of climatic variations in Western Central Asia since AD 618, noting that these high-elevation sites are "exceptionally sensitive to climatic variations" and that "conspicuous interactions exist between [their] ecosystems and climate." This record provides an important perspective on both the Medieval Warm Period and Little Ice Age. Esper et al. note, for example, that early in the seventh century the Medieval Warm Period was already firmly established and growing even warmer. In fact, between AD 900 and 1000 tree growth was exceptionally rapid, at rates that they say "cannot be observed during any other period of the last millennium." Between AD 1000 and 1200, however, growing conditions deteriorated; and at about AD 1500, minimum tree ring-widths were reached that persisted well into the seventeenth century. Towards the end of the twentieth century, ring-widths once again increased; but the scientists say "the twentieth-century trend does not approach the AD 1000 maximum." In fact, there is almost no comparison between the two periods, with the Medieval Warm Period being far more conducive to good tree growth than the Modern Warm Period. As Esper et al. describe the situation, "growing conditions in the twentieth century exceed the long-term average, but the amplitude of this trend is not comparable to the conditions around AD 1000."

Moving further into India, Kar et al. (2002) explore the nature of historical climate change in the Uttarkashi district of Uttranchal in the Western Himalayas at Gangotri Glacier, which is revered as the source of the Holy Ganga. There, based on pollen analyses of a 1.25-meter sediment profile in an outwash plain located some 2-3 km from the glacier's snout, they developed a 2000-year record of regional climate. Between 1700 and 850 years ago, their analysis indicates an "amelioration of climate," as the region ascended from the depth of the Dark Ages Cold Period to the midst of the Medieval Warm Period, after which the climate becomes "much cooler," indicative of its transition to Little Ice Age conditions. In fact, between 300 and 200 years ago, Kar et al.'s data indicate the long-term retreat of the Gangotri Glacier "ceased, possibly with some minor advancement." During the last 200 years, however -- when the study of Esper et al. (2002a) indicates there has been a rather steady warming of the planet -- the glacier's snout has retreated by about 2 km.

In another study from the western Himalayan region of India, Yadav and Singh (2002) developed a spring temperature history based on twelve tree-ring chronologies of Himalayan cedar; and noting that "spring temperature is significantly correlated with mean annual temperature," they say it "to some extent reflects the general temperature variations over the Himalayan region." The "most conspicuous feature" of this history, in the words of the two scientists, was "the long-term cooling trend since the late 17th century that ended early in the 20th century." The abrupt termination of this cooling, which heralded the end of the Little Ice Age, soon thereafter led to the warmest 30-year period (1945-1974) of the past hundred years. However, this warm interval was "well within the range of natural variability," as they describe it. In fact, they report there was an even warmer 30-year period in the latter part of the 17th century, noting further that there was no correlation between their temperature history and that of Mann et al. (1999) prior to the 20th century. The two histories also diverge where their tree-ring reconstructions end. Whereas the instrumental record reported by Mann et al. indicates dramatic warming over the last two decades of the 20th century, the instrumental record reported by Yadav and Singh indicates cooling, as is also indicated by several other studies they cite that are based on both instrumental and tree-ring observations.

Far to the west, in fact beyond the edge of the continent, Schilman et al. (2001) analyzed foraminiferal oxygen and carbon isotopes and the physical and geochemical properties of sediments contained in two cores taken from the bed of the southeastern Mediterranean Sea off the coast of Israel, finding that late Holocene climatic instability was clearly demonstrated by their high-resolution study. Over the past millennium, they make particular mention of two extreme climatic events: one centered at about1200 AD, which they describe as "the Medieval Warm Period global climatic event [our italics]," and one centered at about 1730, which they describe as "the cooling global event known as the Little Ice Age [our italics]."

In discussing their findings, Schilman et al. note there is an abundance of other evidence for the existence of the Medieval Warm Period in the Eastern Mediterranean, including "high Saharan lake levels (Schoell, 1978; Nicholson, 1980), high Dead Sea levels (Issar et al., 1989, 1991; Issar, 1990, 1998; Issar and Makover-Levin, 1996), and high levels of the Sea of Galilee (Frumkin et al., 1991; Issar and Makover-Levin, 1996)," as well as "a precipitation maximum at the Nile headwaters (Bell and Menzel, 1972; Hassan, 1981; Ambrose and DeNiro, 1989) and in the northeastern Arabian Sea (von Rad et al., 1999)." Also, they remark that their Little Ice Age data paint a picture of "the coldest conditions prevailing in the SE Mediterranean during the past 3.6 ka [3600 years]."

Moving back to the east and further south, Doose-Rolinski et al. (2001) analyzed an annually-laminated sediment core extracted from the bed of the northeastern Arabian Sea just south southeast of Karachi, Pakistan, using oxygen isotopes of planktonic foraminifera and measurements of long-chain alkenones to derive a detailed sea surface temperature and evaporation history for the area. The greatest temperature fluctuations of the 5,000-year record occurred between 4600 and 3300 years ago and between 500 and 200 years ago, which periods were also the coldest of the record. Of the latter interval, the authors note that "in northern and central Europe this period is known as the 'Little Ice Age'," and they say their results "confirm [the] global effects" of this cold climatic excursion. Also apparent in their temperature history is a period of sustained warmth that prevailed between about 1250 and 950 years ago, which corresponds nicely with the Medieval Warm Period of northern and central Europe.

In light of the findings of these many reports, it is clear that the Little Ice Age left its imprint over essentially all of Asia. In addition, several of the reports actually refer to this significant climatic anomaly as being of global extent, while openly disagreeing with the revisionist temperature history of Mann et al. (1999) that makes it totally disappear.

Kar, R., Ranhotra, P.S., Bhattacharyya, A. and Sekar B. 2002. Vegetation vis-à-vis climate and glacial fluctuations of the Gangotri Glacier since the last 2000 years. Current Science82: 347-351.

Krenke, A.N. and Chernavskaya, M.M. 2002. Climate changes in the preinstrumental period of the last millennium and their manifestations over the Russian Plain. Isvestiya, Atmospheric and Oceanic Physics38: S59-S79.

Naurzbaev, M.M. and Vaganov, E.A. 2000. Variation of early summer and annual temperature in east Taymir and Putoran (Siberia) over the last two millennia inferred from tree rings. Journal of Geophysical Research105: 7317-7326.

Yang, B., Braeuning, A., Johnson, K.R. and Yafeng, S. 2002. General characteristics of temperature variation in China during the last two millennia. Geophysical Research Letters29: 10.1029/2001GL014485.

Zhang, D.E. 1994. Evidence for the existence of the Medieval Warm Period in China. Climatic Change26: 287-297.